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What is percutaneous absorption?
Absorption of substances from outside of the skin to underneith the skin and into the blood stream
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What are the factors influencing percutaneous absorption?
- Physical and chemical properties
- Pharmaceutical vehicle
- Condition of the skin
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What is the major rate limiting barrier to transdermal drug transport?
Stratum Corneum (Horny Layer)
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WHat is the stratum corneum?
The outer layer of the skin that is composed of partially desiccated non-living cells + film (sebum and sweat) and karatin.
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What layer of the skin is not significant in drug penetration?
The stratum corneum
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What is the layer of skin where the barrier layer with living cells at several differentiated levels?
Stratum lucidum
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What is the living epithelium?
Stratum Lucidum
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What is the layer of skin that is the living epidermis?
Statum Germinativum
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What is the layer of skin that has basal layers separating from dermis?
Stratum Germinativum
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What is the layer of skin that has vascularized tissue that drug must reach?
Dermis
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What is transcellular?
Non-polar drugs that tend to cross cell barrier through lipid rich regions
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What is intracellular?
- Medication that can diffuse through the space between cells
- Channels are the major route of drug penetration
- Polar drugs
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What is trans-appendageal ?
- Accross the skin appendages
- hair follicles
- Sweat Glands
- Sebaceous glands
- Minor drug absorption
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What are the factors relating the drug that affect absorption through the skin?
- Concentration of drug
- Particle size
- Molecular weight
- Solubility in both oil and water
- Attraction to skin
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What the factors relating to the vehicle that affect absorption through the skin?
- Adherence to skin
- Miscibility with sebum
- Action as a moisture barrier (hydration of skin)
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What are the factors relating to the skin that affect absorption through the skin?
- Intact or broken skin
- Surface area applied
- Site of application (thin horny)
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What are the factors relating to the physical factors that affect absorption through the skin?
- Rubbing (inunction)
- Exercise = vasodilation
- Time of contact with skin
- Mutiple applications (saturation)
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What are the chemical methods of enhancing percutaneous absorption?
- Reduction of S. Corneum resistance
- Modification of S. Corneum hydration
- Modification of lipids in intracellular channels
- through carrier mechanism
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What are the solvent, chemical percutaneous enhancers?
- Water
- Alcohol
- Alkyl methyl sulfoxides
- Pyrrolidones
- Laurocapram
- Micellaneous: acetone, dimethyl acetamide, dimethyl formamide
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What are the amphiphies, chemical enhancers?
- Anionic surfactant
- Cationic surfactant
- Amphoteric surfactant
- Nonionic surfactant
- Fatty Acid and alcohol
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What are examples of anionic surfactant?
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What are examples cationic surfactant?
Quaternary ammonium salts, preservative
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What are examples of amphoteric surfactant?
- Lecithins
- Cephalins
- Alkyl betamines
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What are examples of nonionic surfactant?
Mon, di and triglycerides
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What are examples of fatty acids and alcohol for chemical percutaneous enhancer?
- Lauryl
- Cetyl
- Stearyl Alcohol
- Sorbitan
- PEG
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What are the physical methods of enhancers?
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What is ionophoresis?
Delivers a charged chemicals across the skin using eletrical field
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What is sonophoresis?
High-frequency ultrasound facilitates drug penetration through S. Corneum
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What are rate controlling systems intended to do?
- POPICOC
- The drug is release promptly from the system into the S. Corneum for penetration into general circulation
- Systemic Affect
- Cause occlusion of the skin so there is only one way flux of drug, which is a therapuetic advantage over other dosage forms (nothing is loss)
- Design must avoid proliferation of bacteria under occluded skin
- Cause no irritation or sensitization to the skin due to drug, vehicle or adhesive
- Deliver drug at a controlled rate to intact skin without building up in the dermis layer
- Skin is not the targe
- Increase patient compliance
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What are the advantages of TDDS?
- Avoid the GI
- Substitute for oral administration, and parental
- Avoid first pass effect
- Provide mult-day therapy with single patch
- Drug effect terminated when the patch is taking off
- Fast identification of patch during emergencies
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What are the disadvantages of TDDS?
- Can be put on irritating skin
- Only can use potent drugs
- Technical difficulties
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